Table or desk tops are often supported by one or more telescopic supports, such that the table or desk top can be raised or lowered to meet the needs of users. A common application is an overbed table with vertical adjustability, as found in hospitals and the like.
Typically, this functionality is met by providing inner and outer tubes separated by, preferably, a self-lubricating bearing material such as polytetrafluorethylene. While this arrangement provides adequate utility, in order to provide a telescopic support which extends and retracts smoothly, the components need to be manufactured with relatively high precision, which entails substantial costs.
U.S. Pat. No. 4,381,095 (Kritske), issued Apr. 26, 1983, employs an alternate structure having four pairs of rollers spring-mounted to the inner tube and adapted to engage the inner surface of the outer tube. The resistance of the rollers to rolling movement is such that a table surface attached to the telescopic structure only raises or lowers upon application of external force. While this structure can provide for smooth operation, this is contingent upon proper functioning of tensioning springs which extend between the paired rollers, which springs can tend to slacken or even break after extended use. As well, since there exists no positive mechanical connection for locking, table tops supported in this manner can lower unintentionally when heavily loaded.